Solder joint typically includes a nickel bump on one substrate and an electroplated barrier layer on top of a copper pad on another substrate. The electroplated barrier layer is commonly used to protect the copper pad.
There is typically a lack of uniformity in the barrier layer across the copper pad. This lack of uniformity negatively impacts the effectiveness of barrier layer. These barrier layer also usually requires unwanted extra processing steps and increased costs.
In addition, the barrier layer may not be particularly effective in creating a proper solder joint. The copper pad is often totally consumed during the formation of the solder joint. If too much of the copper pad is consumed during formation of solder joint, then the solder joint may form an unreliable electrical connection.